The prior art in the field shows various devices for counting and sorting organisms in water were the object is to give the optimal registration of number and size. These devices are often limited in their capacity of processing large amounts of fish in a short time interval. The relatively unstable concentration of the fish in water, that goes through the handling systems means that they need to be designed to handle peak density. If not, the devices will not be functioning at full capacity during most of the sorting and counting process.
In order to prevent overloading of the equipment, some prior art inventions have solved the problem by reducing the speed of flow towards the counting device and then increase the speed while measurement occurs. International patent application WO 2012/038415 (Wingtech) discloses a system for registration of number and/or weight distribution of marine organisms where an injection duct is connected upstream to the registration container, and an outlet duct connected downstream of the registration container, forming a feed-back loop of fluid. The water is looped around the counting segment in order to increase the velocity within the registration container. International patent application WO 91/03029 (Kvassheim) shows a device for recording of number and size of objects passing between a light source and a camera in free fall.
The prior art does not describe methods that directly control the concentration of living organisms in water in order to minimize the variance and stabilize the concentration which is needed for optimal operation of both counting and sorting devices.
Experience gained by using conventional methods to count and sort fish shows that those methods tend to function best with a low or moderate level of fish concentration. High levels of concentration have a negative effect on both counting and sorting of fish.
When transferring fish in fish-farms between receptacles, it is standard procedure to count the fish in order to keep better control of the batches. A known disadvantage is that while pumping up fish from one container and directing it to another, the concentration of the fish in water is uneven, giving imprecise counting. The fish tend to clump together which gives inexact and misleading counting as some fish overlap others, thus reducing the counted number.